Sanding relay



April 21, 1942. SUDDPTH 2,280,319

- SANDING RELAY Filed July 10, 1941 2 Sheets-Sheet 1 Ihwentor attorneys April 21, 1942.

H. N. SUDDUTH 4 SANDING RELAY Filed July 10, 1941 v2 Sheets-Sheet 2 attorneys 2 Q E Q PH Zmvento;

filo/d044, 54464544 HR I I 4 4 m 50m 3 imm F MD P V the cleanout position in which to the cleanout connection alone.

final cleanout dwell.

Patented Apr. 21, 1942 UNITEDSTATES" PATENT OFFICE Henry Norton Sudduth, Watertown, N. Y., as-

- signor to The New York Air Brake Company,

a corporation of New Jersey Application July 10, 1941, Serial No. 401,829

'1 Claims. (01. 291-3) This invention relates to sanders for high speed railroad trains and particularly to improvements in a relay device described and claimed in the patent to Campbell No. 2,243,244, May 27, 1941. I

The relay described in the Campbell patent above identified is designed to control a sand trap moves towards the sanding position hesitates or dwells in an intermediate cleanout position in which it causes air to be delivered both to the sanding connection and to the cleanout connection ofthe sand trap which it operates.

The effect is to blow the sand delivery hose free i of any obstructions so that free sanding will ocusedmerely to produce a preliminary andvery brief sanding sequence, as is the case in the preferred embodiment described in the Campbell patent, the volume of the timing reservoir is small and hence exercises no seriously disturbing efiect on the final cleanout dwell of the relay, but where this relay is used to produce sanding cycles of considerable duration, say ninety seconds,as" is also proposed'in the Campbell patent, the volume of the timing'chamber is much larger, and when added .to the volume of the delay chamber which forms a part of the relay increases unduly the second or final cleanout dwell of the relay.

The purpose of the present invention is so to relate the timing chamber to the relay mechanism that the timing chamber is allowed to percur when the relay completes its full traverse and reaches sanding position. In that position the relay causes air tobe delivered to the sanding connectionalone, the cleanout connection being vented. On the return traverse from sanding toward running position, the relay also dwells in air is delivered The purpose of the present invention is closely related tothis second dwell which, under certain To understand this problem, it is necessary to explain the way in which the relay is controlled. i

The Campbell patent shows two control mechanisms for the relay. One of these is an electrically actuated admission and exhaust valve which is controlled through a train circuit from the head end of the train. This electrically controlled mechanism imposes no undue delay in the In certain instances the electrical mechanism may be omitted altogether as is fully explained in the Campbell patent. However, it is often used and will be included in the disclosure of the present application to illustrate that it may be used without interfering with the successful operation of the present invention.

The second control for the relay is a pneumatically operated admission and exhaust valve ume of a timingreservoir. Where the relayis form its normal function in limiting the overall duration of the sanding cycle without materially increasing the final cleanout dwell of the relay.

Basically, the idea is to impose on the slide valve mechanism of the relay an asymmetric characteristic or sequence such that the timing chamreaches final cleanout position. Specifically the invention contemplates the use of ports in the slide valve of the relay which perform this function, and, according to the preferred embodiment,

perform it byquickly charging the timing chamber t9 suspend its timing function. At this time the timing chamber is isolated from the delay chamber which is thus allowed to remain incontrol of the final cleanout dwell. y g

The invention willnowbe described by reference to the accompanying drawings in which:

Fig, 1 is a diagram of the braking and sanding equipment for one car of a train.

Fig. 2is .a diagrammatic section of the relay valve including its electrical and pneumatic controls. (The parts are shown in running or inactive position).

Figs. 3, 4 and 5 are diagrams of the slide valve components of the relay showing respectively preliminary cleanout position, sanding position, and final cleanout position.

' It may be remarked that Fig. 1 shows a car equipment similar to that of Fig. 2 of the Campbell patent and thus represents the equipment for cars other than the motor car.

The system can be controlled by mechanism such. as that shown in Fig. 1 of the Campbell patent; it can be controlled as indicated in Fig. 9

of the Campbell patent, and in fact is available for use generally wherever the structure of the Campbell patent might be used and with improved results.

The sand trap with which the relay is intended to be used is shown in the Campbell Patent No. 2,243,243, and an examination of this patent will give a full understanding of the cleanout and sanding characteristics of such a trap.

Refer'first to Figs. 2 to 5 inclusive which views are diagrams to the extent that the ports are drawn as if they all lay in a common plane which is the plane of section.

The entire relay is carried on a pipe bracket II which is supported on the car and to which all pipe connections are made. The sanding'air line appears at l2, the cleanout, air line at I3, the sanding supply reservoir connection, which furnishes all operating air, at l4, and the timing reservoir connection at l5. The connection I6 is from the sanding port of the control valve, as will be explained, and is the connection through which the relay is put into action by port l1, and the bracket encloses a chamber [8 which participates in a timing function hereinafter described.

Mounted on one side of the bracket II is a housing l9 which encloses the pilot slide valve mechanism of the relay as well as the piloted poppet-valves. In the upper portion of the housing 19 are mounted a slide valve chamber bushing 2| and a cylinder bushing 22. Working in the cylinder 22 is a piston 23 which has a stem 24 extending intothe slide valve chamber within bushing 2| and terminatingin the spider 25 which guides the stem. Mounted for lost motion between the shoulder 26 adjacent the piston and. the spider 25 isthe main slide Valve 21. This has wings 28 which straddle the piston stem 24 and which carry a bow spring 29 arranged to hold the valve 21 against its seat. Between the wings 23 the back of the *slide valve 21is-formed with-a seat for-a graduating slide valve 3|, which is closely confined between the shoulders 32 and 33 on stem 24 so that the graduating valve partakes of all of the movements of the piston 23.

Piston 23 is urged to the right by a duplex spring assembly so arranged that only one of its two concentric springs resists the motion of the piston to the left through that part of its travel corresponding to the lost motionof the piston relatively to the main slide valve 21. At the limit of such motion both springs oppose motion of the piston.

The main or primary spring is shown at 34 and is confined under stress between an inner spring seat 35 and an outer cupped spring seat 36. These two spring seats are connected together by a headed stem 31 which is slidable through a bushing 38. This in turn is slidable axially through the spring seat 36.for a limited range corresponding to the lost motion just mentioned. The spring seat 35.seats within the end of a closure cap 39 which. closes the 'outer end of the cylinder 22. The cap is sealed by a gasket, as shown, and the gasket projects inward far enough to serve as a seat for the piston when the latter arrives at the outer limit of its motion.

The secondary spring 4| is a lighter spring mounted concentrically within the spring 34. It is sustained at its outer end on the cupped spring seat 42, which is thimble-like in form, engages the end of bushing 38 and telescopes over the spring seat 36. Its telescoping motion is limited by the bushing 38. The action is as follows: When the piston 23 moves outward, it is opposed initially by the spring 34 until the spider '25 engages the slide valve 21 and is about to .move it. At this point bushing 38 and spring seat 42 reach their limit of motion. From then on the'resistance of the inner spring 4| is added to that ,of the spring 34. The purpose is to cause the piston to pause momentarily at the limit of motion of the graduating valve 3| relativelyto the slide valve 21. This effect is had in both directions of motion.

The space within valve chamber bushing 2| and to the right of the piston-23 is in free communication with the sanding reservoir passage M. It is also in communication, by way of filter 4-3 and choke 44, with a passage 45 in bracket H which communicates with the chamber l8 already described. From. the space within the cap 39 to the left of piston 23, a passage 46 leads'through the body l9 and bracket H, as shown.

In the seat on which the main slide valve 21 is mounted are four ports; a cleanout air control port 4'1, a branch of the exhaust port l1, a sanding air control port 48, and a delay suppression port 50 which is one of the principal features of the present invention. In the valve 21 and communicating with the port 48 in all positions of the slide valve is a through port 49. Anenlargement at the bottom of the port 49 -is the means to maintain communication between it and the port 48 in all positions of the slide valve 21. Also formed'through the slide valve 21 is a port 5| which is enlarged at its bottom so that it communicates with the exhaust port H in all positions of the slide valve. This port has an extension 52 leading outward and thence to the graduating valve seat in the back. of the slide valve. In addition there are two impulse ports 53 and 54 which lead through the slide valve. There is also'a delay suppression port 60 which coacts with the port 50 and leads through the slide valve 21.

The graduating valve has two cavities in its lower face, namely 55 and 56, and has drilled through it an impulse port 51.

These ports are so arranged that in the normal orrunning position of- Fig.2 cleanout control port 41'is connected to exhaust port H by way of port 53 and cavity 55, port 52 and port 5|. At the same time the sanding air control port 48 is connected to exhaust port 11 by port 49,'cavit'y 53-and port 5|, and port 51 communicates with the port 54 which is then blanked at the seat. The port Bil is exposed at its upper end-of the graduating valve but is blanked at the seat.

Vfhen the piston starts outward the graduating valve 3| exposes port 49 at the same time that port 51 opens to port 53 and the ports are fully open at the limit of lost motion of the graduating valve relatively to the slide valve.

The port is in this position blanked at both ends. The effect is toadmit air under pressure from the sanding supply reservoir to both the ports 41 and 48 (see Fig. 3). I

The remaining movement of the piston 23' outward moves the slide valve and carries port 53 out of register with port 41, cutting off theflow of airto port 41 and'causing port 54, to register with port 41 (seeFig. 4). In the position of Fig.

4, port 60 has moved into register with port 58,

but is blanked at its upper end by the graduating valve. 1 I

On the return excursion the upper endof port 60 is exposed by the inward movement of the graduating valve and at the same time the graduating valve first closes the port 49 after which the port 51 registers with the port 54 (see Fig.

5) to furnish a cleanout blast to the port 41. Asabove set forth, the piston pauses in the position of Fig. 5 because at this point the spring 4| reaches its limit of expansion. Exposure of the closed and the valve 16 is unseated to admit air port 60, which is then in register withport 50,

admits air from the slide valve chamber to the port 50 to limit the dwell in the position of Fig. 5,. by means which will be later explained in detail. Continued movement carries the slide valve inward so that port 54 moves out of register withport 41 and port 60 moves out of register with port 50.

When running position (Fig. 2) v isreached, both'ports 41 and 48 are vented to atmosphere by connection with port II as al- .ready described.

I the cap 6| and the housing I9 and connected at' its center to a thrust plate 63 which carries an exhaust poppet valve 64. The space immediately above the diaphragm 62 is connected to atmosphere by way of port I1.

When the diaphragm is in its normal lower positionthe valve 64is open and connects the chamber 65, to which the cleanout air line I3 leads, with atmosphere. When pressure fluid isadmitted beneath diaphragm 62 the efiect is to force the valve 64,upward, closing the exhaust passage. A lug on the end of the valve 64 strikes a similar lug on the lower end of a poppet valve 66 and unseatsthisvalve against the opposition of a coil compression spring 61 and fluid pressure communicated from the sanding supply I reservoir line I4 to the chamber 68 above the poppetvalve 66. Similarly, the sanding to the space within cap 1| and beneath flexible diaphragm 12. This is clamped at its periphery between the cap 1| and the housing I9 and is clamped at its center to the thrustplate 13, to which the exhaust valve 14, similar to the valve 64, is attached. The'chamber15 is connected to the sanding air line I2 and the valve 14 carries a lug which, when the valve is forced closed, strikes a similar lug on the inlet valve 16 and forces it upward against the resistance of the coil compression spring .11 and the pressure communicated to the chamber 18 by the sanding supply passage I4.

from the sanding reservoir connection directly to the sanding connection I2. In this way a relatively small slide valve mechanism, with ports of comparatively small size, pilots the action of inlet and exhaust mechanisms of large capacity.

Electric control is exercised by energizing and de-energizing a winding 8| which is mounted urrder a cap 82 on a valve body 83 bolted to bracket II. In the housing 83 is a chamber 84 which is in free communication by way of port with the chamber I8 already described. The

port-46 leading from the space to the left of piston 23 terminatesin valve chamber 85. In the chamber 851s a double beat poppet valve having an exhaust head 86 which coacts with an atmospheric exhaust seat 81' and, an inlet head 88 which coacts with the supply seat89 controlling flow between the chambers 84 and 85.

A coil compression spring 9| urges the poppet valve toward the exhaust seat. When the winding 8| is de-energized. as it is under running conditions, the exhaust head 86 of the double beat valve seals on seat 81 and the port 46 is connected by way of chamber 84 and port 45 with the chamber i8, and further by way of choke 44 and filter 43 with the slide valve chamber within bushing 2 I. As explained, this chame ber is in free communication with the sanding supply reservoir line I4. Thus, under normal conditions, the pressures on the two sides of the piston 23 equalize and the springs force the piston 23 to its innermost or right-hand position, shown in Fig. 2.

If the winding 8'] is energized, the doublebeat poppet valve is moved downward, isolating chamber 85 from chamber 84 so the chamber I8, re-.

control port 48 leads mains charged, and connecting chamber 85 with atmosphere through a flow restricting choke 92. It follows that the space to the left of piston 23' is vented to atmosphere at a rate controlled by the flow capacity of choke 92. The piston moves outward against the resistance of spring 34 and just at the limit of lost motion between the piston and the main slide valve 21. the resistance of the second spring 4| is added, so that the piston pauses momentarily in that position and then resumes its outward excursion until it seals on the cap gasket. This is sanding position (see Fig. 4).

When the winding 8| is de-energized, the double beat poppet valve as, as will return to the o sition shown in Fig. 2,. closing the exhaust from chamber 85 and connecting chamber 85 with chamber 84 and chamber l8. The resulting increase of pressure on the outer face of piston 23 will start the return excursion of the piston. Under these conditions the choke 44 will exert control on the rate of development of pressure on I the left side of piston 23 and consequently on Thus the twopassages I2 and I3 are normally I vented to atmosphere by the poppet valves 64 and 14. If the port 41 is put underlpressure, the

exhaust passage is closed and a direct connec- The connection I6 leads to a chamber IOI within the cap I92 and below a diaphragm I03. This is clamped at its periphery between body 96 and cap I02 and is connected at its center to the thrust plate I04. Slidably mounted within the thrust plate I04 and limited in its outward motion by a stop flange is a plunger I05 which isurged outward by the coil compression spring I06. When the diaphragm I03 is forced upward, plunger I05 reacts against an exhaust poppet valve I01 to urge it in an exhaust closing direction. The pilot of the exhaust valve I01 is in position tocollide with the pilot of the reversely seated poppet valve I08, which is urged closed by a coil compression spring I09 and which controls flow from the chamberl I3. Chamber II3 is in free communication with the port 50 and is in restricted communication with the delay chamber I8 by way of a flow restricting choke I I I and a ball check valve II2 which is so arranged as to permit flow from the chamber I8 to the chamber H3 and close against reverse flow.

The connection l6 leads from the sanding port of the brake controlling valve device and when pressure is developed in connection I6 the diaphragm I03 moves upward, forcing the valve I07 closed and the valve I08 open, The effect is to reduce the pressure in the chamber I8 and since this is normally connected by way of port 45, chamber 84, chamber 85 and port 46, with the space to th left of the piston 23, the resulting reduction of pressure in chamber I8 causes the piston 23 to move outward.

This reduction of pressure will continue until timing reservoir 99 is charged nearly to equalization with the sanding supply passage I l. Choke 44 feeds to chamber l8 at a rate less than the outflow through the larger choke III. Ultimately development of pressure in chamber I8 would cause piston 23 to move inward and terminate sanding. This would occur after an interval.determined by the combined volume of the chambers I8 and 99, say ninety seconds. Actual sanding ends when the graduating valve reaches the position of Figure 5 in which it blanks the port 49 and exposes the port 60. Exposure of the port 60 causes air to flow from the slide valve chamber to the chamber H3 and since the valve I08 is then open, the effect is to charge not only the chamber H3 but also the timing reservoir 99 to supply pressure. This seats the check valve H2 tightly so that charging of the delay chamber I8 alone through the choke 44 times the dwell. Thus, the dwell in the final cleanout position of Fig. 5 is determined by the time necessar to charge the delay chamber I8 instead of both the delay chamber and the timing reservoir. In consequence the dwell in Fig. 5 is of practically the same duration as it would be were control exercised through the winding 8 I 1 It will be observed that it is still necessary to charge the timing reservoir 99 but that the charging of this reservoir shortens the dwell in the cleanout position of Fig. 5 and thus reduces the wasteful consumption of cleanout air.

The use of a relatively large reservoir 99 to secure long sanding cycle would unduly increase the dwell in the position of Fig. 5 if it were necessary, as in the Campbell device, to charge not only the chamber I8 but also the timing chamber 99 while the parts remain in the position of Fig. 5.

Reference will now be made to Fig. l. The brake pipe appears at I26 and would be connected from car to car in atrain byflexible hose with couplings and angle cocks shown in the drawing, all in accordance with conventional practice. The brake pipe I29 is connected through the usual cut-out cock and dust collector with the brake controlling valve device I21, here assumed to be a control valve of the D-22 type. Such valves may be used either in an automatic or combined straight air automatic system but for purposes of explanation a simple automatic system is assumed.

The control valve I21 has three connections to chambers in a multi-chambered reservoir I28. These connections are the auxiliary reservoir connection I29, the emergency reservoir connection I3 I, and the displacement volume connection I32. The brake pipe I26 is normally under pressure (say lbs. per sq. in.) and the control valve I21 functions in release position to charge the auxiliary and emergency reservoirs and also to deliver air to a supply reservoir connection I33 which is in communication with the supply reservoir I34.

From the reservoir I34 the pipe I35 leads to the intercepting valve I36 and from the intercepting valve I39 another pipe I3? leads to the sander supply reservoir 38 to which the pipe It already mentioned is connected. The intercepting valve is controlled by pressure in the pipe I39 in such a way that when the pipe I32 is under pressure, as it is during a brake application, the reservoir I 30 cannot draw on the reservoir I34 for air. Thus the brake supply reservoir is protected against depletion of charge by demands of the sanding system, as soon as a brake application commences. The structure of the intercepting valve I30 is not shown but it is fully described in the Campbell patent, above identified.

The control valve I21, in response to a reduction of brake pipe pressure, will establish related pressure in the pipe I lI leading to the admission and exhaust relay valv'eWZ. The relay valve functions to establish-proportionate pressures in the pipe I43 and in the connected brake cylinders I A l. The relay I 42 is supplied with air from the reservoir I34 through the pipe I33.

A pair of sand traps I 55 are shown and are illustrated as connected to the sanding air connection I2 and the cleanout air connection I3 in the usual manner. The pipe It leads from the sander control connection of the control valve I 21 and is connected to the sanding relay as already described. The control valve I21 may put the sanding connection it under pressure in emergency application or in both service applications and emergency applications, so far as the present invention is concerned.

The winding 8| in the housing 82 is connected across electrical train circuits I46, I41. These are connected from car to car by jumpers I48 in the usual manner. The electrical controlling mechanism may be actuated in any known Way, for example, it may be operated from the head of the train as proposed in the Campbell patent, above identified. Furthermore, the electrical mechanism can be wholly omitted, in which event the relay would be operated pneumatically under the control of the mechanism in the housing 96. As explained, a long timing cycle requires a large volume for the timing reservoir 99 and where the timing cycle is long, the volume of the timing reservoir 99 added to the volume of the delay chamber I8 permits too long a dwell in the final cleanout position of Fig. 5.

The eifect of applicants invention is to isolate the reservoir 99 and charge it fully as soon as the relay arrivesin the position of Fig. 5, so that the: excess dwell :is notimposed but ,onthe contrary the controlis determined solely, by Jthe volumeof the delay chamber |8.

wA's'pointed out in theCampbell patent, above identified, a. sanding operation initiated by the mechanism, in th'ewhousing 96 cannot be terminated short of itstime period; by operation of the electrical mechanism controlled ibyg winding' 8L. However, it can be ,prolonged by that mechanismg j i 1 r While" the relay has been described in considerable, detail and while references havev been made to a particulartype-of sandtrap and a particular arrangement or vinterconnection of the T sanding and braking system; it should be understoodthatthis isintended to be illustrativeand not limiting. The inventionj is useful with any timing relay "having lsimilar.characteristics of timing control, and in which the timing is effected chamber in somewhat less restricted communication, withsaid-delay; chamber and {connected with said delay suppression port;-;a check valve piston working in said cylinder andgseparating the -slide valve chamber from aflworking space in i said cylinder; a slide valve mechanism in the slide valve chamber, connected to be actuated by said piston, said valve mechanism having opposite limiting'positions, one of which is an-inactive running position andtheothera sanding; position,rthe valve having further intermediate cleanout positions one, for each direction of shift between said limiting positions; loading means for biasing the piston and valve mechanism toward running position and for causing them to dwell in saidintermediate positions; a delay chamber forming an enlargement of said work ing space; means affording restricted communication between said delay chamber and the slide valvechamber; a timing chamber; valve means normally venting said timing chamber, and operable to close such vent andplace the timing chamber in restricted communication with said delay chamber; and means rendered effective by said valve mechanism in one only of said intersaid cylinder; a slide valve and coacting graduating valve connected to be actuated by said 1 piston, one valve having lost motion relatively to the other, there being arunning position at the limit of piston motion inward toward the valve chamber in which the sanding and cleanout ports are vented, a sanding position at the outward limitof piston motion in which the sanding port is charged and the cleanout port vented, and cleanout positions one in each direction of shift between such limiting positions in each of which at least the cleanout port is under pressure, said valves controlling a delay suppression port and serving to close such port in all positions except cleanout position assumed during inward shift; loading means for biasing said piston and valves toward running position and for I causing themto dwell in said cleanout positions;

controlling the last, named restricted communicationiand inhibiting flow toward; the delay chamber; 3 a timinggchamber; and valve means normally serving tovent said timing chamber and operable to close said, vent and'connect the-tim ing chamber and delay suppression chamber.

L3. In a sander relay the combination of a sander valvehaving asanding position, anda with fluid under pressure'above a definite value and; toward sanding iposition when said pressure 3 is substantially reduced; a delay chamber; means 1 chambers togethemand means controlled by said relay valve and serving as the latter moves; from sanding to running position tocharge' thetimin'g '1 chamber and isolate it from the delay chamber.

which sanding is suspended; a movable abutment,

connected to shift said valve in reverse directions between said limiting positions; means forming a working space on one side of said abutment; force developing means associated with said abutment for biasing said abutment and valve toward running position when said working space i is charged with fluid under a normal pressure and toward sanding position when said pressure is substantially reduced; means for charging said working space with pressure fluid 'at a restricted rate; a timing chamber; means affording a restricted communication between the working space and the timing chamber, theflow capacity of such communication exceeding the restricted charging flow to the working space; controlling valve means having a normal position in'which it closes the communication between, said timing chamber and working space and connects the timing chamber to exhaust, said valve means being shiftable to an active position in which said exhaust is closed and the working space is oonnected through said restricted communication with the timing chamber; and means c0ntrolled by said relay valve and serving as the relay valve moves from sandingto running po- P sition while said controlling valve means is in i said active position to isolate the timing chamher from the workingspace and charge the timing chamber.

' a movable abutment connected to shift said valve between said positions; means forming a working space at one side of said abutment; force developing means associated with said abutment for biasing-said abutment and valve toward running'position when said working'space is charged with fluid under pressure above a definite value and toward sanding position when said pressure is substantially reduced; means for supplying pressure fluid to said working space at a rest'r'icted' rate; a timing chamber; controlling means normally connecting the timing chamber to theexhaust but operable to close said exhaust and connec'tthe timing chamber with said working space; means for operating said controlling means; and means controlled by said sander valve and rendered effective by approach thereof to running position to charge and isolate said timing reservoir." v I 69111 a sanding relay unit, the combination of a housing enclosing aslide valve chamber and a communicating cylinder; means for supplying air under pressure to said slide valve chamber; a-piston working insaid cylinder and separating the slide valve chamber from a working space in said cylinder; a slide valve and coacting graduating valve connected to be actuated by said piston; one valve having lost motion relatively toithe other, there being a running position at the limit of" piston motion inward toward the valve chamber in which the-sanding and cleanout ports are vented, a sanding position at the outward limit of piston motion in which the sanding port ischar'ged and the cleanout port is vented, and cleanout positions one in each direction of shift between such limiting positions in each of which at least the cleanout port is under pres* sure, said valves controlling a delay suppression port 'and serving to close such port in all positionsex'cept the cleanout position assumed during inward'shiit; loading means for biasing said piston and valves toward running position and for causing them to dwell in said cleanout positions; a delay chamber forming an enlargement of said working space; means affording restricted communication between said delay chamber and said slide valve chamber; a timing chamber; valve means normally venting said timing chamber, and operable to close such vent and place the timing chamber in restricted communication with said delay chamber; one-way flow means for resisting flow from said timing chamber to said delay chamber and a connection between the timing chamber and said delay suppression port for charging said timingchamber in cleanout position during inward shift.

7. In a sander relay the combination of a sander valve having a sanding position, and a running position in which sanding is suspended; a movable abutment connected to shift said valve between said positions; means forming a working space at one side of said abutment; force-developing means associated with said abutment for biasing said abutment and valve toward running position when said working space is charged with fluid under pressure above a definite value and toward sanding position when said pressure is substantially reduced; means for charging said working space with pressure fluid at a restricted rate; a timing chamber; controlling means normally serving to isolate said working space from said timing chamber and connect the timing chamber to' exhaust but operable to close said exhaust and connect the timing chamber and working space together; and means controlled by said relay valve and serving as the latter moves from sanding to running position to charge the timing chamber and isolate it from the working space.

HENRY NORTON SUDDUTH. 

